Method of preparing a glass release surface employing a perfluorosilane for manufacturing an anti-lacerative window assembly

ABSTRACT

An improved method of preparing a glass release surface useful in the manufacture of anti-lacerative window assemblies is disclosed. The glass surface is treated with a perfluorosilane such as (Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane, and thereafter may be easily released from the polyurethane layer of an anti-lacerative window assembly. The release agent (Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane is particularly useful under severe laminating conditions such as high temperature and pressure over a long period of time. Its use imparts excellent optical properties to the polyurethane layer.

FIELD OF THE INVENTION

This invention relates generally to the field of treating glass toproduce a release surface for releasing thermoplastic polyurethanes; andmore particularly to the treatment of a glass cover plate for releasinga thermoplastic polyurethane surface, useful in the manufacture ofanti-lacerative window, e.g., automotive windshield, assemblies.

BACKGROUND OF THE INVENTION

The art of laminating layers of glass and interposed polymeric materialsto produce "safety glass" laminates has been practiced for many years bythe manufacturers of automobile windshields. Such composites effectivelyreduced the serious injuries that had previously resulted from bodilyejection from an automobile through a shattered single pane windshieldupon impact during an accident. However, the glass and polymer, i.e.,polyvinyl butyral, composites still were likely to cause severelacerations and cosmetic disfigurement due to flying pieces of brokenglass or bodily contact with the windshield.

Thereafter, anti-lacerative windshields were developed, having one ormore layers of glass substrate and a layer of polymeric material bondedto the inside surface of the windshield facing the passengercompartment. This configuration provided a substantial improvement insafety by placing a shock absorbent layer of material between the glasswindshield and the automobile passengers. It eliminated the likelihoodof flying glass particles within the passenger compartment upon impactduring an accident, and provided a body impact surface that aided thedeceleration of a person thrust against the windshield, thereby reducinghis or her susceptibility to lacerations. In addition, it reducedlaceration by avoiding direct body contact with broken glass.

Although several methods exist for the bonding of a polymeric materialto the inner surface of an automobile windshield, the art has notdeveloped into an industry-wide standard because of the problemsencountered in producing an optically transparent laminate. Morespecifically, manufacturers have found it difficult to form the exposedsurface of the polymeric material so that it is at all points parallelto the surface of the glass substrate, and optically clear.

One method of manufacture involves the use of a glass cover plate whichsubstantially conforms to the predetermined curvature of a glasswindshield substrate. The cover plate is contacted to the surface of afilm of thermoplastic polyurethane, which in turn is intimatelycontacted to a glass windshield substrate. Pressure is applied to thecover plate in order to laminate the thermoplastic polyurethane film tothe glass windshield substrate, and to impress a smooth, opticallytransparent surface onto the surface of the polyurethane layer. Such anoperation requires a release agent which allows the cover plate toeasily and cleanly part from the polyurethane layer, following alaminating process employing severe conditions of high temperature andpressure over a long period of time, without affecting the smooth imageimpressed by the cover plate onto the polyurethane layer.

SUMMARY OF THE INVENTION

The present invention provides a solution to the aforementioned problem.I have discovered that a perfluorosilane, including a preferred(Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane is asuperior parting agent, the perfluorosilane being effective under severelaminating conditions of high temperature and pressure over a longperiod of time, for glass in intimate contact with thermoplasticpolyurethanes. Additionally, the perfluorosilane of the presentinvention is functional as a parting agent between glass and thermosetpolyurethanes. Dodecyltriethoxysilane and octadecyltriethoxysilane havebeen found to be ineffective as parting agents under severe laminatingconditions as sometimes encountered in the manufacture of windshields,e.g., 250° F. to 325° F., 215 psig to 275 psig, for periods of 25 to 55minutes.

Glass treated with(Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane effectivelyreleases thermoplastic polyurethane when employed in press laminatingprocesses using high temperatures, for example 285 degrees F., and highpressures, for example 225 psig, for long periods of time, for example45 minutes. The(Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane is directlyapplied to the surface of the glass plate, which then contacts thepolyurethane. This intersection defines the release surface along whichthe glass plate and polyurethane material may be parted.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Release agents are essential in the manufacture of anti-lacerativewindshields which require that an optically clear finish be formed onthe surface of the thermoplastic polyurethane layer facing the passengercompartment of an automobile. A thermoplastic polyurethane film istypically laminated to a glass windshield substrate by applying pressureto the polyurethane film which, by means of a preapplied primer, bondsto the glass windshield substrate. The pressure directed toward thesurface of the thermoplastic polyurethane film is generally effectuatedthrough a glass cover plate which substantially conforms to thepredetermined curvature of the glass windshield substrate. A releaseagent must be interposed between the cover plate and thermoplasticpolyurethane film in order for a clean separation to occur after thelaminating process. Determining the proper release agent is particularlydifficult when the laminating process is carried out under severeconditions such as high temperature and pressure over a long period oftime. The release agent must be easy to apply under commercialmanufacturing conditions, have no detrimental effect on the physical orchemical properties of the polyurethane layer, and accurately reproducethe smooth surface finish of the glass cover plate.

According to the present invention, a superior release surface resultsfrom the application of a perfluorosilane, preferably(Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane, to glass,which is thereafter intimately contacted to the thermoplasticpolyurethane. The glass is treated by wiping the(Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane onto thesurface in one or more applications, followed by drying at roomtemperature or with the aid of a convection oven.

The use of the perfluorosilane such as(Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane has severaladvantages over existing release agents. It is simply applied by wipingonto a glass cover plate in smooth strokes. This suggests minimalexpenditures for the manufacturing equipment necessary for large scaleproduction of anti-lacerative windshields. The perfluorosilane releaseagent may be handled and cured at ambient temperatures, also implyingreduced manufacturing costs. Finally, the use of perfluorosilane resultsin a thermoplastic polyurethane surface having optical propertiessuperior to those produced by many existing release agents.

The present invention comprises a release agent preferably containingapproximately 1.0 to 15 percent by weight of a perfluorosilane such as(Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane in asuitable solvent. Alcohols are desirable solvents, and more particularlyisopropanol is preferred.

A glass cover plate, utilized for applying pressure to the thermoplasticpolyurethane surface in a polyurethane-and-glass prelaminateanti-lacerative windshield assemblage, the surface features of whichwill be reproduced on the exposed surface of the thermoplasticpolyurethane layer, is prepared. The solution of the perfluorosilanesuch as (Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane inan appropriate solvent is preferably applied to the glass cover plate bywetting an absorbent towel and wiping the solution onto the releasesurface of the cover plate in smooth longitudinal strokes, then buffedperpendicularly to the direction of application. However, othermechanical methods of application that produce a uniform coating may beemployed. The cover plate is then preferably heated by placing it into aforced air convection oven for approximately fifteen minutes to twohours, at a temperature of approximately 50 to 120 degrees C., afterwhich it is removed from the oven and allowed to cool to roomtemperature. It must be understood that the operation of heating thecover plate need not be performed in order to form the release surface;allowing the cover plate to stand at room temperature for a period ofapproximately fifteen minutes to four hours will likewise establish therelease surface. Although it is preferable to make a single applicationof the (Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilanesolution, the aforementioned steps, including treating the glass surfaceand heating the cover plate, may be repeated.

The (Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane treatedglass release surface of the present invention is useful for releasingthe thermoplastic polyurethane layer of an anti-lacerative window.Parting of the glass cover plate and the polyurethane layer is achievedwith minimal mechanical force and results in an optically transparentanti-lacerative window.

Those polyurethanes which are useful in the practice of the presentinvention are generally described as the reaction products of apolyisocyanate and a polyol, as for example disclosed in U.S. Pat. No.3,900,686 to Ammons et al.

The preferred polyisocyanate is 4,4'-methylene-bis-(cyclohexylisocyanate), which is commercially available from the E. I. du Pont deNemours and Company under the trademark Hylene W. Other suitablealiphatic diisocyanates include, but are not limited to,4,4'-isopropylidene-bis-(cyclohexyl isocyanate), 1,4-cyclohexyldiisocyanate, 1-4-tetramethylene diisocyanate, and 1,6-hexamethylenediisocyanate. Although not preferred, other polyisocyanates includinghydrogenated aromatic diisocyanates, mixtures of cycloaliphatic andstraight chained aliphatic diisocyanates and/or aromatic diisocyanates,and substituted diisocyanates, as well as thioisocyanates, may be used.

The polyisocyanates listed above are reacted with at least one polyolhaving at least two functional groups which are reactive with theisocyanate groups and chain extender diol such as butane diol. Typicalpolyols include polyester diols and polyether diols, preferably having anumber average molecular weight of approximately 500 to 5000.

The preferred polyester diols utilized for producing polyurethanes inthe present invention are represented by the reaction products of analiphatic dicarboxylic acid having for example adipic, succinic,glutaric, palmitic or suberic functional components, with a suitablealiphatic diol such as ethylene glycol, 1,3-propanediol, 1,4-butanediolor 1,6-hexanediol. Polyester diols useful for the preparation ofpolyurethanes used in the present invention may additionally be formedby the reaction of caprolactone monomers, including gamma-carprolactone,delta-caprolactone, epsilon-caprolactone, monoalkyl or dialkylcaprolactone, with a suitable glycol such as ethylene glycol, diethyleneglycol, triethylene glycol, 1,4-butanediol or 1,6 hexanediol.

The preferred polyether diols utilized for producing polyurethanes inthe present invention include, but are not limited to polytetramethyleneglycol ether, polytrimethylene glycol ether, polypentamethylene glycolether and polyhexamethylene glycol ether.

The thermoplastic polyurethane film is positioned in intimate surfacecontact with the inboard surface of a glass windshield substrate, towhich a primer has been applied for the bonding of the polyurethane filmto the glass windshield substrate. The previously prepared glass coverplate, which has substantially the same predetermined curvature of theglass windshield substrate, is positioned with its treated surface inintimate surface contact with the exposed surface of the polyurethanefilm.

Conventional means for compressing and heating the assemblage, therebyurging the glass cover plate toward the glass windshield substrate, areemployed. This causes the thermoplastic polyurethane film to bond to theglass windshield substrate. The release agent is particularly effectiveunder the severe laminating conditions of high temperature, for example285 degrees F., and high pressure, for example 225 psig, over a longperiod of time, for example 45 minutes.

Thereafter, the glass cover plate is parted from the polyurethane layerof the anti-lacerative windshield laminate along the boundary defined bythe intersection between the polyurethane film and the glass cover platethe surface of which has been treated with the(Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilanetriethoxysilaneparting agent according to the present invention. The disclosure of aprocess for manufacturing and method of assembling anti-lacerativewindshields is described in U.S. Pat. No. 3,808,077 to R. G. Rieser etal.

EXAMPLE 1

An anti-lacerative laminate was produced by first assembling into astacked relationship an outboard glass sheet, a sheet ofpolyvinylbutyral and an inboard glass sheet. The inner surface of theinboard glass sheet (that is to say, the surface not facing thepolyvinylbutyral sheet) was treated with a three percent by weightsolution of gamma-aminopropyltriethoxysilane in isopropanol as a primerfor adhesion of a thermoplastic polyurethane film. The solution wasapplied by wetting an absorbent towel and wiping the solution onto thesurface in smooth strokes. The stacked assemblage was allowed to standat room temperature for thirty minutes.

A clean glass cover plate, having substantially the same predeterminedcurvature and surface area as the stacked laminate assemblage, wastreated with a three percent by weight solution of(Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane, referred toas perfluorosilane, in isopropanol. The solution was applied to therelease surface of the cover plate by wetting an absorbent towel andwiping the solution onto the cover plate in smooth longitudinal strokes,then buffing the cover plate perpendicularly to the direction ofapplication. The cover plate was heated by placing it in a forced airconvection oven for one hour at 93 degrees C., then removed from theoven and allowed to cool to room temperature. Thus, the release surfacewas prepared for utilization.

A thermoplastic polyurethane film, produced by the reaction of4,4'-methylene-bis-(cyclohexyl isocyanate) (HYLENE W) and an adipic acidpolyester extended with 1,4-butanediol, was prepared for bonding to theinboard glass sheet. Suitable thermoplastic polyurethanes arecommercially available from K. J. Quinn & Company, Inc. under theproduct code designation PN-03 and PE-192. The thermoplasticpolyurethane film was positioned in intimate surface contact adjacentthe treated surface of the inboard glass sheet, and the treated releasesurface of the cover plate was positioned in intimate surface contactadjacent the opposing surface of the polyurethane film.

A vacuum bag was sealed around the perimeter of the stacked,prelaminated assemblage. The assemblage was laminated under severeconditions by placing same in an oil autoclave for 45 minutes at 285degrees F. and 225 psig pressure. The autoclave was cooled to roomtemperature, and the assembly removed. The vacuum bag was removed andthe cover plate parted from the anti-lacerative laminate.

Many laminates were produced by this method, and each possessedexcellent optical qualities.

EXAMPLE 2

The relative releasing ability of release agents can be demonstrated byobserving the contact angle of a drop of water on a surface formed byapplication of the release agent to glass.* It has been found that to beacceptable for coating a glass cover plate to be employed in bondingpolyurethane to glass and use of the resulting structure in automotivevision areas the contact angle should be at least 85°, and preferably90°. Excellent results are obtained when utilizing a release agent forthe manufacture of windshields under severe laminating conditions if thecontact angle is at least 93° to 95°:

    ______________________________________                                        Contact Angle for Release Agents                                                               Carbon Chain                                                                             Contact Angle                                     Release Agent    Length     Degrees                                           ______________________________________                                        Perfluorosilane  C10        93                                                Octadecyltriethoxysilane                                                                       C18        79                                                Dodecyltriethoxysilane                                                                         C12        55                                                None             --         28                                                ______________________________________                                    

These examples serve to illustrate the present invention; however, itmust be understood that the present invention may be practiced otherwisethan as specifically described without departing from the scope of thefollowing claims.

I claim:
 1. A method of providing an optically transparent,anti-lacerative windshield assembly for a motor vehicle, the methodcomprising the steps of:(a) assembling into a stacked relationshipindividual layers including a transparent glass substrate sheet having apredetermined curvature, a thermoplastic polyurethane anti-lacerationfilm abutting one surface of the glass substrate sheet, a glass coverplate having substantially the same curvature as the glass substratesheet and abutting the polyurethane film on its side opposite the glasssubstrate sheet; (b) coating the glass cover plate with(Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane on its sideadjacent the polyurethane film, prior to assembly with the glasssubstrate sheet and polyurethane film; (c) compressing the stackedassemblage; and (d) releasing the glass cover plate from thepolyurethane layer without marring the surface of the polyurethanelayer, to provide an optically transparent, anti-lacerative windshieldassembly.
 2. A method as defined in claim 1, in which a solution ofapproximately 1 to 15 weight percent of(Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane in a solventis coated onto the glass cover plate, and the coating dried prior tocompression of the assemblage.
 3. A method as defined in claim 1, inwhich the stacked assemblage is compressed by evacuating air frombetween the layers of the assemblage and placing the assemblage in anautoclave for from 25 to 55 minutes at a temperature between 250° F. to325° F. and a pressure between 215 psig to 275 psig.
 4. In a method ofproducing an optically transparent anti-lacerative window assemblycomprising:(a) assembling into a stacked relationship individual layersincluding a transparent glass substrate sheet having a predeterminedcurvature, a thermoplastic polyurethane anti-laceration film abuttingone surface of the glass substrate sheet, and a glass cover plate havingsubstantially the same curvature as the glass substrate sheet andabutting the polyurethane film; and (b) compressing the stackedassemblage by evacuating air from between the layers of the assemblageand thereafter placing the assemblage in an autoclave, the glass coverplate providing optical properties to the polyurethane layer; theimprovement comprising applying a solution of approximately 1 to 15weight percent of(Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane in a solventto the surface of the cover plate abutting the polyurethane film andthereafter drying same before compressing the stacked assemblage toprevent adherence of the cover plate to the polyurethane layer, andoperating the autoclave with the assemblage therein for from 25 to 55minutes at a temperature between 250° F. and 325° F. and a pressurebetween 215 psig to 275 psig thereby producing an optically transparentwindow assembly in which the polyurethane layer has good opticalproperties and good anti-lacerative properties.
 5. A method as definedin either of claims 4 or 1, in which a solution of about 3 percent byweight of (Heptadecafluoro-1,1,2,2-Tetrahydrodecyl)-1-Trichlorosilane isused to coat the glass cover plate.
 6. A method as defined in either ofclaims 4 or 1, in which the polyurethane is a polyester polyurethane. 7.A method as defined in either of claims 4 or 1, in which thepolyurethane is a polyether polyurethane.
 8. A method as defined ineither of claims 1 or 2, in which the stacked assemblage is compressedby evacuating air from between the layers of the assemblage and placingthe assemblage in an autoclave for 45 minutes at 285° F. under 225 psigpressure.